Track information generating device, track information generating method, and computer-readable storage medium

ABSTRACT

Track information generating devices, methods, and programs acquire a self-contained navigation track of a vehicle indicated by time-series pieces of self-contained navigation information, and acquire a GPS track that is a track of the vehicle indicated by time-series pieces of GPS information. The devices, methods, and compare the self-contained navigation track with the GPS track to acquire a first correction amount for obtaining the highest degree of coincidence between the self-contained navigation track and the GPS track and then correct the self-contained navigation information using a second correction amount that is smaller than the first correction amount.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No 2010-142604 filed onJun. 23, 2010 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique for generating trackinformation that indicates the track of a vehicle.

2. Description of the Related Art

In an existing art, there is known a technique that acquires anestimated current position of a vehicle through self-containednavigation based on the results detected by a direction sensor and adistance sensor. For example, Japanese Patent Application PublicationNo. 2000-298028 (JP-A-2000-298028) describes a technique in which anestimated current position of a vehicle is acquired on the basis of theresults detected by a direction sensor and a distance sensor, theestimated current position is compared with candidate positions on aroad to determine the most probable candidate position on the road andthen the estimated current position is corrected on the basis of themost probable candidate position on the road. In addition,JP-A-2000-298028 describes a technique for determining an error circleto narrow candidate positions on a road on the basis of an estimatedcurrent position and a position measured by a GPS.

SUMMARY OF INVENTION

A direction sensor and a distance sensor used for self-containednavigation as described in the existing technique respectively detect adirection difference from a reference direction and a distance from areference position, so an estimated current position is inaccurate whenthe reference direction or the reference position is inaccurate. Inaddition, accumulated errors of each sensor increase over time, so anestimated current position is more inaccurate as the vehicle deviatesfrom the reference direction and/or the reference position. Then, in theexisting technique, a candidate position is set on a road on the basisof an estimated current position and then a correction is performed sothat the candidate position is assumed as the estimated currentposition. However, the estimated current position acquired by thesensors contains an error, so the correction is not always right. Then,once an erroneous correction is performed, it is difficult to correctthe estimated current position to a right current position because ofpieces of information detected by the sensors are relative displacementsfrom references, such as the reference direction.

The present invention provides a technique for improving the accuracy ofa self-contained navigation track.

A first aspect of the invention provides a track information generatingdevice. The track information generating device includes: aself-contained navigation track acquisition unit that acquires aself-contained navigation track that is a track of a vehicle, indicatedby time-series pieces of self-contained navigation information; a GPStrack acquisition unit that acquires a GPS track that is a track of thevehicle, indicated by time-series pieces of GPS information; and aself-contained navigation information correcting unit that compares theself-contained navigation track with the GPS track to acquire a firstcorrection amount for obtaining the highest degree of coincidencebetween the self-contained navigation track and the GPS track and thento correct the self-contained navigation information using a secondcorrection amount that is smaller than the first correction amount.

According to the first aspect, the self-contained navigation informationis corrected using the second correction amount that is smaller than thefirst correction amount for obtaining the highest degree of coincidencebetween the self-contained navigation track and the GPS track. By sodoing, it is possible to avoid a situation that a position and adirection indicated by the self-contained navigation information totallydiffer from a true position and a true direction and to suppress theinfluence of an erroneous correction. Thus, it is possible to easilyimprove the accuracy of the self-contained navigation track.

A second aspect of the invention provides a track information generatingmethod. The track information generating method includes: acquiring aself-contained navigation track that is a track of a vehicle, indicatedby time-series pieces of self-contained navigation information;acquiring a GPS track that is a track of the vehicle, indicated bytime-series pieces of GPS information; and comparing the self-containednavigation track with the GPS track to acquire a first correction amountfor obtaining the highest degree of coincidence between theself-contained navigation track and the GPS track and then to correctthe self-contained navigation information using a second correctionamount that is smaller than the first correction amount.

A third aspect of the invention provides a computer-readable storagemedium that stores computer-executable instructions for performing atrack information generating method. The track information generatingmethod includes: acquiring a self-contained navigation track that is atrack of a vehicle, indicated by time-series pieces of self-containednavigation information; acquiring a GPS track that is a track of thevehicle, indicated by time-series pieces of GPS information; andcomparing the self-contained navigation track with the GPS track toacquire a first correction amount for obtaining the highest degree ofcoincidence between the self-contained navigation track and the GPStrack and then to correct the self-contained navigation informationusing a second correction amount that is smaller than the firstcorrection amount.

According to the above second and third aspects, as well as the firstaspect, it is possible to improve the accuracy of the self-containednavigation track.

BRIEF DESCRIPTION OF DRAWINGS

The features, advantages, and technical and industrial significance ofthis invention will be described below with reference to theaccompanying drawings, in which like numerals denote like elements, andwherein:

FIG. 1 is a block diagram of a track information generating device;

FIG. 2A and FIG. 2B are flowcharts that show a self-contained navigationinformation correcting process;

FIG. 3 is a flowchart that shows the process of comparing a GPS trackwith a self-contained navigation track;

FIG. 4A to FIG. 4C are views for illustrating rotation and translationof the self-contained navigation track;

FIG. 5A to FIG. 8B are views for illustrating a statistical process fordetermining direction differences and a representative value of thedirection differences;

FIG. 9A to FIG. 11B are views for illustrating a statistical process fordetermining position differences and a representative value of theposition differences;

FIG. 12 is a flowchart that shows a self-contained navigationinformation correcting process;

FIG. 13A is a view that illustrates a manner of correcting aself-contained navigation position; and

FIG. 13B is a view that illustrates a manner of correcting aself-contained navigation direction.

DETAILED DESCRIPTION OF EMBODIMENTS

Here, embodiments of the invention will be described in accordance withthe following sequence.

-   (1) Configuration of Track Information Generating Device-   (2) Track Information Generating Process-   (2-1) Map Matching Process-   (2-2) Self-contained Navigation Information Correcting Process-   (3) Alternative Embodiments

(1) Configuration of Track Information Generating Device

FIG. 1 is a block diagram that shows the configuration of a trackinformation generating device 10 according to an embodiment of theinvention. The track information generating device 10 includes a controlunit 20 and a storage medium 30. The control unit 20 includes a CPU, aRAM, a ROM, or the like. The control unit 20 executes programs stored inthe storage medium 30 or the ROM. In the present embodiment, the controlunit 20 executes a navigation program 21. The navigation program 21 hasthe function of determining the position of a vehicle on a road throughmap matching process on the basis of self-contained navigationinformation and then displaying the position of the vehicle on a map. Inthe present embodiment, the navigation program 21 executes trackinformation generating process that generates track informationindicating the track of the vehicle through a plurality of techniquesand, particularly, has the function of generating a self-containednavigation track on the basis of the self-contained navigationinformation with high accuracy.

Map information 30 a is recorded in the storage medium 30 in advance.The map information 30 a is used to, for example, determine the positionof the vehicle. The map information 30 a includes node data, shapeinterpolation point data, link data, object data, and the like. The nodedata indicate the positions, or the like, of nodes set on roads on whichthe vehicle travels. The shape interpolation point data are used todetermine the shape of a road between the nodes. The link data indicatea link between the nodes. The object data indicate the positions, types,and the like, of objects present on the roads or around the roads. Notethat, in the present embodiment, the link data include information thatindicates the width of the road corresponding to each link.

The vehicle equipped with the track information generating device 10according to the present embodiment includes a user I/F unit 40, avehicle speed sensor 41, a gyro sensor 42 and a GPS receiving unit 43.In addition, the navigation program 21 includes a self-containednavigation track acquisition unit 21 a, a matching track acquisitionunit 21 b, a GPS track acquisition unit 21 c and a self-containednavigation information correcting unit 21 d. The navigation program 21cooperates with the vehicle speed sensor 41, the gyro sensor 42 and theGPS receiving unit 43 to execute the function of generating aself-contained navigation track on the basis of pieces of self-containednavigation information with high accuracy.

The vehicle speed sensor 41 outputs a signal corresponding to therotational speed of wheels equipped for the vehicle. The gyro sensor 42outputs a signal corresponding to an angular velocity exerted on thevehicle. The self-contained navigation track acquisition unit 21 a is amodule that causes the control unit 20 to implement the function ofacquiring a self-contained navigation track that is a track of thevehicle, indicated by time-series pieces of self-contained navigationinformation. That is, the control unit 20 operates the self-containednavigation track acquisition unit 21 a to acquire the output signals ofthe vehicle speed sensor 41 and gyro sensor 42 via an interface (notshown) as self-contained navigation information.

Here, in the operation of the self-contained navigation trackacquisition unit 21 a, it is only necessary to acquire a self-containednavigation track, and, for example, it is only necessary to indirectlyacquire time-series positions and directions of the vehicle in such amanner that the time-series output signals of the sensors equipped forthe vehicle are acquired to detect the behavior of the vehicle andthereby determine the displacements in the relative position anddirection with respect to a reference. The behavior of the vehicle to bedetected may be various physical quantities of the vehicle. For example,it is conceivable that sensors that acquire a vehicle speed, anacceleration, an angular velocity, and the like, are equipped for thevehicle and a self-contained navigation track is acquired from signalsoutput from the sensors.

Then, the control unit 20 determines the position displacement of thevehicle from the reference position on the basis of the output signal ofthe vehicle speed sensor 41 to determine the current position of thevehicle, and determines the direction displacement of the vehicle fromthe reference direction on the basis of the output signal of the gyrosensor 42 to determine the current direction of the vehicle. Note that,in this specification, the position of the vehicle, determined on thebasis of the output signal of the vehicle speed sensor 41, is termed aself-contained navigation position, and the direction of the vehicle,determined on the basis of the output signal of the gyro sensor 42, istermed a self-contained navigation direction. Note that the abovedescribed reference position and reference direction just need to be theposition of the vehicle and the direction (traveling direction) of thevehicle that are determined at predetermined time, and, for example, maybe the position of the vehicle and the direction of the vehicle that aredetermined from GPS information (described later) at predetermined time.Furthermore, the control unit 20 determines self-contained navigationpositions and self-contained navigation directions at multiple timepoints to determine pieces of information that indicate time-seriesself-contained navigation positions and time-series self-containednavigation directions, and then acquires the determined pieces ofinformation as a self-contained navigation track.

The matching track acquisition unit 21 b is a module that causes thecontrol unit 20 to implement the function of executing map matchingprocess in which a road of which the shape indicated by the mapinformation 30 a most coincides with the self-contained navigation trackis assumed as a road on which the vehicle is traveling and thenacquiring a matching track that is the time-series track of the vehicle,determined through the map matching process. That is, the control unit20 consults the map information 30 a to check the shapes of roadspresent around the vehicle against the self-contained navigation track.Then, the control unit 20 determines the road having the highest degreeof coincidence between the shape of the road and the self-containednavigation track and then assumes the determined road as a road on whichthe vehicle is traveling to thereby determine the position and directionestimated as the position and direction of the vehicle on that road asthe position and direction of the vehicle.

Note that, in this specification, the position of the vehicle,determined through the above described map matching process, is termed amatching position and the direction of the vehicle, determined throughthe map matching process, is termed a matching direction. Furthermore,the control unit 20 determines matching positions and matchingdirections at multiple time points to determine pieces of informationthat indicate time-series matching positions and matching directions,and then acquires the determined pieces of information as a matchingtrack.

Then, the control unit 20 displays the matching position, the matchingdirection and the matching track on the user I/F unit 40. That is, theuser I/F unit 40 is an interface unit for the user to input instructionsor to provide various pieces of information to the user. The user I/Funit 40 has a display unit, a button, a speaker, or the like (notshown). In the present embodiment, the control unit 20 displays a map onthe display unit of the user I/F unit 40, and displays icons indicatingthe matching position, the matching direction and the matching track onthe map. Therefore, the control unit 20 generates image data thatindicate the map and the icons indicating the matching position, thematching direction and the matching track, and outputs the image data tothe user I/F unit 40. The user I/F unit 40 displays the map and theicons indicating the matching position, the matching direction and thematching track on the display unit on the basis of the image data.

Note that the control unit 20 operates the matching track acquisitionunit 21 b to determine the degree of reliability of each of the matchingposition and the matching direction that are determined through the mapmatching process. In the present embodiment, the control unit 20determines the degree of reliability of the matching position on thebasis of the width of the road on which the vehicle is assumed to betraveling, determined through the map matching process, and determinesthe degree of reliability of the matching direction on the basis ofvariations in the direction of the vehicle in process of executing themap matching process.

The GPS track acquisition unit 21 c is a module that causes the controlunit 20 to implement the function of acquiring a GPS track that is atrack of the vehicle, indicated by time-series pieces of GPSinformation. That is, the control unit 20 operates the GPS trackacquisition unit 21 c to cause the GPS receiving unit 43 to acquire GPSinformation for calculating the current position and current directionof the vehicle to thereby determine the position and direction of thevehicle on the basis of the GPS information. Note that, in thisspecification, the position of the vehicle determined on the basis ofthe GPS information is termed a GPS position, and the direction of thevehicle determined on the basis of the GPS information is termed a GPSdirection. The control unit 20 further determines GPS positions and GPSdirections at multiple time points to determine pieces of informationthat indicate time-series GPS positions and time-series GPS directions,and then acquires the determined pieces of information as a GPS track.Note that GPS information in the present embodiment includes GPSaccuracy information that indicates the accuracy of the GPS information.

The GPS track acquisition unit 21 c just needs to be able to acquire aGPS track on the basis of time-series GPS information. Thus, the GPStrack acquisition unit 21 c just needs to be able to acquire signalsfrom GPS satellites and then determine the current position and currentdirection of the vehicle in a prescribed coordinate system on the basisof the acquired signals. Note that the prescribed coordinate system maybe a coordinate system consisting of latitude and longitude, acoordinate system consisting of longitude, latitude and altitude, or thelike.

In the present embodiment, GPS accuracy information consists of an indexacquired together GPS information and an index acquired on the basis ofthe state of the vehicle. That is, GPS information decreases in accuracybecause of the relative relationship between the GPS satellites and thevehicle and the influence of a communication environment (degree ofmultipath, or the like). The GPS information includes an index (dilutionof precision (DOP), such as horizontal dilution of precision (HDOP), thenumber of satellites placed in a state or position where high-accuracypositioning is possible, or the like) that indicates a decrease inaccuracy. Then, in the present embodiment, the control unit 20 operatesthe GPS track acquisition unit 21 c to acquire GPS accuracy information,included in the GPS information, together with the GPS information.

In addition, the accuracy of GPS information depends on the state of thevehicle, so, in the present embodiment, the control unit 20 alsoacquires an index that indicates the degree of decrease in the accuracyof GPS information due to the state of the vehicle. Specifically, thecontrol unit 20 operates the GPS track acquisition unit 21 c to acquireoutput information of the vehicle speed sensor 41 and output informationof the gyro sensor 42 and then acquire an index, as GPS accuracyinformation, such that the accuracy of GPS information decreases as thespeed of the vehicle decreases and the accuracy of GPS informationdecreases as the maximum variation in the direction of the vehicle in apredetermined period of time increases. Note that, in the presentembodiment, GPS accuracy information is determined for each of a GPSposition and a GPS direction, and the accuracy of a GPS position isdetermined on the basis of an accuracy index included in the GPSinformation. In addition, the accuracy of a GPS direction (GPS satellitedirection described later) is determined on the basis of the accuracyindex included in the GPS information and the degree of decrease in theaccuracy of the GPS information due to the state of the vehicle. Notethat, in the present embodiment, GPS accuracy information is normalizedso that the highest accuracy is 100 and the lowest accuracy is 0 foreach of a GPS position and a GPS direction.

As described above, the present embodiment is configured so that amatching position and a matching direction are acquired while checking aself-contained navigation track against a matching track to display thematching position, the matching direction and the matching track on theuser I/F unit 40. Furthermore, in the present embodiment employs, inconsideration of the respective characteristics of the self-containednavigation track, matching track and GPS track, the self-containednavigation track is corrected using the matching track or the GPS track.

The matching position and matching direction displayed on the user I/Funit 40 are a position and direction that are determined by checking theself-contained navigation track against the road shape. Therefore, whenthe self-contained navigation track is inaccurate, the matching positionand the matching direction are also inaccurate. Specifically, inself-contained navigation, the position displacement of the vehicle fromthe reference position is determined on the basis of output informationof the vehicle speed sensor 41 to determine a self-contained navigationposition, and the direction displacement of the vehicle from thereference direction is determined on the basis of output information ofthe gyro sensor 42 to determine a self-contained navigation direction.That is, the self-contained navigation is a navigation to indirectlydetermine the position and direction of the vehicle within theprescribed coordinate system consisting of latitude, longitude, and thelike, so the self-contained navigation cannot directly acquire aposition in the prescribed coordinate system. Thus, when the referenceposition of the self-contained navigation position and the referencedirection of the self-contained navigation direction are inaccurate, theposition and direction of the self-contained navigation track areinaccurate, so a position and a direction that are totally differentfrom a true position and a true direction may be detected as a matchingposition and a matching direction. In addition, self-containednavigation information contains an error due to the behavior, or thelike, of the vehicle. An error of output information of the vehiclespeed sensor 41 and an error of output information of the gyro sensor 42accumulate over time, so the self-contained navigation position and theself-contained navigation direction decrease in accuracy over time. Inthis case as well, a position and a direction that are totally differentfrom a true position and a true direction may be detected as a matchingposition and a matching direction.

On the other hand, GPS information directly indicates a position and adirection within the prescribed coordinate system consisting oflatitude, longitude, and the like. Thus, even when the GPS informationmay contain an error, the latitude and longitude of the GPS informationare reliable within an error range. Therefore, a position and adirection that are totally different from a true position and a truedirection are not detected as GPS information. Then, when theself-contained navigation information is corrected so as to reduce thedifference between the self-contained navigation track and the GPStrack, it is possible to avoid a situation that a position and adirection that are indicated by the self-contained navigationinformation are totally different from a true position and a truedirection.

Note that, although it is less reliable to set one sample GPSinformation as a correction target because an error of GPS informationis poor in regularity and may steeply vary, it is possible tostatistically enhance the reliability of the position and direction withan increase in total frequency when time-series pieces of GPSinformation are collectively considered. Then, when a time-seriesself-contained navigation track is compared with a time-series GPS trackand then the self-contained navigation information is corrected so as toreduce the difference between the self-contained navigation track andthe GPS track, it is possible to reduce accumulated errors of theself-contained navigation track, and it is possible to suppress anincrease in accumulated errors over time.

Furthermore, the node data, shape interpolation point data, and thelike, included in the map information 30a indicate positions on actuallypresent roads in latitude, longitude, and the like, so a matchingposition and a matching direction may be an actual position and anactual direction on a road. Thus, when the self-contained navigationinformation is corrected so as to reduce the difference between theself-contained navigation track and the matching track, the position anddirection indicated by the self-contained navigation information may becorrected to at least an actually present position and an actuallypresent direction.

In light of such characteristics of the tracks, in the presentembodiment, the control unit 20 operates a self-contained navigationinformation correcting unit 21 d to set one of the GPS track and thematching track, having a higher degree of reliability, as a correctiontarget track and then to correct the self-contained navigationinformation so as to reduce the difference between the self-containednavigation track and the correction target track. That is, a GPS trackand a matching track directly indicate positions and directions withinthe prescribed coordinate system, so the GPS track and the matchingtrack can be a reference used to correct a self-contained navigationtrack that indirectly indicates positions and directions. Then, one ofthe GPS track and the matching track, having a higher degree ofreliability, is selected as a correction reference of the self-containednavigation information. By so doing, it is possible to correct theself-contained navigation track with reference to information having ahigher degree of reliability among pieces of information obtained in thevehicle. As a result, it is possible to effectively improve the accuracyof the self-contained navigation track. Note that, in the presentembodiment, the matching track acquisition unit 21 b is operated toacquire the degree of reliability of a matching track, and theself-contained navigation information correcting unit 21 d is operatedto acquire the degree of reliability of a GPS track. The details ofthese degrees of reliability will be described later.

Self-contained navigation information just needs to be corrected so asto reduce the difference between a self-contained navigation track and acorrection target track. In the present embodiment, the control unit 20rotates and translates a self-contained navigation track so as to obtainthe highest degree of coincidence between the self-contained navigationtrack and a correction target track, sets a correction target of theself-contained navigation information on the basis of the rotated andtranslated track and then corrects the self-contained navigationinformation so as to reduce the difference from the correction target.Note that, when the correction target track is a matching track, thecorrection target set through the above rotation and translation issubstantially equivalent to a matching position and a matchingdirection. That is, when the correction target track is a matchingtrack, the position of the correction target is the matching position,and the direction of the correction target is the matching direction.

When the correction target track is a GPS track, the self-containednavigation track is rotated and translated so as to obtain the highestdegree of coincidence between the self-contained navigation track andthe GPS track. That is, the control unit 20 compares the self-containednavigation positions and self-contained navigation directions obtainedthrough rotation and translation of the self-contained navigation trackin a state where the shape of the self-contained navigation track ismaintained with GPS positions and GPS directions, and then assumes thestate where the differences between the multiple positions and themultiple directions are minimum as the state where the degree ofcoincidence is the highest. As a result, the rotation angle andtranslation amount of the self-contained navigation track compared withthe GPS track are determined, and the control unit 20 assumes the resultobtained by adding the rotation angle to the current self-containednavigation direction and adding the translation amount to the currentself-contained navigation position as a correction target.

The control unit 20 operates the self-contained navigation informationcorrecting unit 21 d to correct the output information of the vehiclespeed sensor 41 and the output information of the gyro sensor 42 so thatthe self-contained navigation position and the self-contained navigationdirection approach the correction target determined as described above.Here, the self-contained navigation position and the self-containednavigation directions determined on the basis of the output informationof the vehicle speed sensor 41 and the output information of the gyrosensor 42 just need to be corrected, and, of course, the referenceposition and the reference direction may be corrected instead. Notethat, in the present embodiment, the self-contained navigationinformation correcting unit 21 d repeatedly corrects the self-containednavigation position and the self-contained navigation direction so as toapproach the correction target, and the self-contained navigationinformation correcting unit 21 d is configured so that theself-contained navigation position and the self-contained navigationdirection do not coincide with the correction target at the time of eachcorrection.

That is, when a correction amount for correcting a self-containednavigation position and a self-contained navigation direction tocoincide with a correction target is a first correction amount, thecontrol unit 20 is configured to correct self-contained navigationinformation using a second correction amount that is smaller than thefirst correction amount. As described above, once a self-containednavigation track is corrected erroneously, it is difficult to recorrectthe self-contained navigation position and/or the self-containednavigation direction. Then, in the present embodiment, the secondcorrection amount that is smaller than the first correction amount isused to correct the self-contained navigation information to therebysuppress the influence of the correction even if an erroneous correctionis performed. Thus, it is possible to easily improve the accuracy of theself-contained navigation track. Note that the second correction amountis smaller than the first correction amount and just needs to be set soas to achieve part of a correction achieved by the first correctionamount.

(2) Track Information Generating Process

Next, track information generating process implemented by the navigationprogram 21 will be described. The track information generating processimplemented by the navigation program 21 is executed at an interval of apredetermined period of time, and self-contained navigation informationcorrecting process that improves the accuracy of a self-containednavigation track is executed in process of executing the above trackinformation generating process. FIG. 2A and FIG. 2B are flowcharts thatshow the self-contained navigation information correcting process. Onthe other hand, the control unit 20 operates the matching trackacquisition unit 21 b at a predetermined period of time in parallel withthe self-contained navigation information correcting process. Here,first, the map matching process will be described.

(2-1) Map Matching Process

In the map matching process, the control unit 20 operates the matchingtrack acquisition unit 21 b to acquire the map information 30 a and aself-contained navigation track and then checks the map information 30 aagainst the self-contained navigation track. That is, the control unit20 operates the self-contained navigation information correcting unit 21d to acquire the output information of the vehicle speed sensor 41 andthe output information of the gyro sensor 42 and then determinedisplacements in position and direction of the vehicle after thesepieces of output information are acquired last time. Then, the controlunit 20 determines a self-contained navigation position and aself-contained navigation direction on the basis of accumulated positiondisplacements from the reference position and accumulated directiondisplacements from the reference direction, and sets time-seriesself-contained navigation positions and time-series self-containednavigation directions, which are determined within a predeterminedperiod of time, as a self-contained navigation track. Note that thereference position and the reference direction may be updated over time;however, the initial value of the reference position and the initialvalue of the reference direction are determined on the basis of GPSinformation, or the like.

In addition, the control unit 20 consults the map information 30 a toacquire link data, node data and shape interpolation point data thatindicate the shapes of roads present within a predetermined range aroundthe self-contained navigation position. Then, the control unit 20 checksthe self-contained navigation track against the pieces of data acquiredfrom the map information 30 a to determine the road of which the shapemost coincides with the self-contained navigation track.

Subsequently, the control unit 20 operates the matching trackacquisition unit 21 b to acquire a matching track. That is, the controlunit 20 assumes the road, of which the shape most coincides with theself-contained navigation track, as a road on which the vehicle istraveling, and then rotates and translates the self-contained navigationtrack so that the shape of the road that is assumed as a road on whichthe vehicle is traveling most coincides with the self-containednavigation track. Then, the control unit 20 sets the positioncorresponding to the latest self-contained navigation position in therotated and translated self-contained navigation track as a matchingposition, and sets the traveling direction of the vehicle at thematching position on the road as a matching direction. Furthermore, thecontrol unit 20 acquires time-series matching positions and time-seriesmatching directions, which are determined within a predetermined periodof time, as a matching track.

Furthermore, the control unit 20 acquires the degree of reliability ofthe matching track. In the present embodiment, the degree of reliabilityof a matching position and the degree of reliability of a matchingdirection are acquired by different techniques. That is, the controlunit 20 sets the degree of reliability of the matching position on thebasis of the distance that the vehicle is assumed to be traveling on acontinuous road and the width of the road on which the vehicle isassumed to be traveling. In the present embodiment, the accuracy of amatching position is defined in five levels as shown in the followingTable 1. That is, when the distance that the vehicle is assumed to betraveling on a continuous road (matching continuous distance) is shorterthan or equal to a predetermined distance Ts (m), the control unit 20sets the degree of reliability of the matching position at 1. When thematching continuous distance is longer than the predetermined distanceTs, the control unit 20 sets the degree of reliability of the matchingposition at any one of 1 to 5. Then, in order to set the degree ofreliability of the matching position in further details when thematching continuous distance is longer than the predetermined distanceTs, the control unit 20 consults the link data of the map information 30a to determine the width of the road that is assumed as a road on whichthe vehicle is traveling. Then, the control unit 20 sets the degree ofreliability of the matching position at 5 when the road width is smallerthan or equal to a predetermined threshold T4, and sets the degree ofreliability of the matching position at 4 when the road width is largerthan the predetermined threshold T4 and is smaller than or equal to apredetermined threshold T3. Furhter, the control unit 20 sets the degreeof reliability of the matching position at 3 when the road width islarger than the predetermined threshold T3 and is smaller than or equalto a predetermined threshold T2, and sets the degree of reliability ofthe matching position at 2 when the road width is larger than thepredetermined threshold T2 and is smaller than or equal to apredetermined threshold T1. The control unit 20 sets the degree ofreliability of the matching position at 1 when the road width is largerthan the predetermined threshold T1. That is, the control unit 20increases the degree of reliability of the matching position as thewidth of the road that is assumed as a road on which the vehicle istraveling reduces.

TABLE 1 MATCHING DEGREE OF CONTINUOUS RELIABILITY OF DISTANCE ROAD WIDTHPOSITION SHORTER THAN OR — 1 EQUAL TO Ts LONGER THAN Ts T4 OR BELOW 5 T3OR BELOW 4 T2 OR BELOW 3 T1 OR BELOW 2 OTHER THAN 1 ABOVE

Furthermore, the control unit 20 sets the degree of reliability of thematching direction on the basis of the distance that the vehicle isassumed to be traveling on a continuous road and the variation in thedirection of the vehicle in process of executing the map matchingprocess. In the present embodiment, the accuracy of a matching directionis defined in five levels. That is, the control unit 20 sets the degreeof reliability of the matching direction at 1 when the distance that thevehicle is assumed to be traveling on a continuous road (matchingcontinuous distance) is shorter than or equal to a predetermineddistance Ts (m), and sets the degree of reliability of the matchingdirection at 2 or above when the matching distance is longer than thepredetermined distance Ts. In order to set the degree of reliability ofthe matching direction in further details when the matching continuousdistance is longer than the predetermined distance Ts, the control unit20 determines a variation in the direction within a last predeterminedperiod of time on the basis of the output information of the gyro sensor42 within the last predetermined period of time. Then, the control unit20 sets the degree of reliability of the matching direction at 3 whenthe variation in the direction is smaller than a predetermined thresholdTd, and sets the degree of reliability of the matching direction at 2when the variation in the direction is larger than or equal to thepredetermined threshold Td. That is, the control unit 20 increases thedegree of reliability of the matching direction as the variation in thedirection in process of executing the map matching process reduces.

TABLE 2 VARIATION IN MATCHING DIRECTION WITHIN DEGREE OF CONTINUOUSPREDETERMINED RELIABILITY OF DISTANCE PERIOD OF TIME DIRECTION SHORTERTHAN OR — 1 EQUAL TO Ts LONGER THAN Ts BELOW Td 3 Td OR ABOVE 2

In the present embodiment, as described above, the degree of reliabilityof a matching position and the degree of reliability of a matchingdirection are set by different techniques. However, in a specific case,the degree of reliability of a matching position and the degree ofreliability of a matching direction are set by the same technique. Thatis, the degree of reliability of a matching position and the degree ofreliability of a matching direction are respectively set on the basis ofthe above described Table 1 and Table 2 when the vehicle is traveling ona normal road; however, it is impossible to acquire GPS information in atunnel, so a technique different from the method based on Table 1 andTable 2 is employed so that a matching track easily becomes a correctiontarget track.

Specifically, when the vehicle is assumed to be traveling on a road in atunnel, the control unit 20 operates the matching track acquisition unit21 b to determine the shapes of roads within a predetermined rangearound the vehicle by consulting the node data, shape interpolationpoint data and link data included in the map information 30 a and todetermine the degree of coincidence of the direction by checkingdirections at multiple positions on a road (traveling directions whenthe vehicle travels on a road) against time-series self-containednavigation positions. Then, the degree of reliability of a matchingposition and the degree of reliability of a matching direction are setso as to increase as the degree of coincidence of the directionincreases. Note that the degree of coincidence of the direction may bedetermined using a variance of the direction, or the like. The abovedescribed degree of reliability of a matching position and the abovedescribed degree of reliability of a matching direction are respectivelyset each time the latest matching position and the latest matchingdirection are determined.

In addition, the above configuration is one example. The degree ofreliability of a matching position and the degree of reliability of amatching direction may be set by analyzing the degree of coincidence ofthe position, and a similar process when the vehicle travels on a roadin a tunnel may be executed in a parking lot in which GPS informationcannot be acquired. Furthermore, the degree of reliability of a matchingposition and the degree of reliability of a matching direction are thedegree of reliability of information obtained as a result of the mapmatching process, so the degree of reliability of a matching positionand the degree of reliability of a matching direction may be decreasedwhen the accuracy of the map matching process may decrease. For example,when it falls within a predetermined period of time after the vehiclestarts traveling (the power is turned on) or there is another probablecandidate road (for example, an acute branch road or a parallel road)within a predetermined distance around the road that is assumed as theroad on which the vehicle is traveling, when the difference between thedirection indicated by the output information of the gyro sensor 42 andthe direction of a road is larger than or equal to a predetermined valueor when the road that is assumed as the road on which the vehicle istraveling is situated in an attached facility of an expressway (servicearea, parking area, or the like), the degree of reliability of amatching position and the degree of reliability of a matching directionmay be decreased or may be set to a certain lower value (degree ofreliability is 1, or the like), for example.

(2-2) Self-Contained Navigation Information Correcting Process

In the self-contained navigation information correcting process shown inFIG. 2A and FIG. 2B, the control unit 20 operates the GPS trackacquisition unit 21 c to acquire pieces of GPS accuracy information(step S100). Subsequently, the control unit 20 executes the process ofcomparing a GPS track with a self-contained navigation track (stepS105). The process of comparing a GPS track with a self-containednavigation track is a process of acquiring the degree of reliability ofa GPS track and a first correction amount (rotation angle andtranslation amount) for obtaining the highest degree of coincidencebetween the self-contained navigation track and the GPS track, and isimplemented by the flowchart shown in FIG. 3. In addition, FIG. 4A toFIG. 4C are views for illustrating rotation and translation of aself-contained navigation track in a coordinate system in whichlongitude is set to x-axis and latitude is set to y-axis.

FIG. 4A shows an example of a self-contained navigation track Tn by thesolid curved arrow. FIG. 4B shows an example of a GPS track by the solidcircles and the arrows. That is, in FIG. 4B, each of the solid circlesindicates a GPS position Gp, each of the solid straight arrows indicatesa GPS satellite direction Gds at the corresponding GPS position Gp, andeach of the broken straight arrows indicates a GPS intercoordinatedirection Gdc between the adjacent GPS positions Gp. GPS informationincludes information indicating the direction of the vehicle; however,not the direction of the vehicle but the direction of an interpositionvector of the vehicle may be assumed as the direction of the vehicle.Then, in the present embodiment, the direction of the vehicle includedin GPS information is termed a GPS satellite direction, the direction ofan interposition vector of the vehicle is termed a GPS interpositiondirection, and a GPS direction is evaluated on the basis of both the GPSsatellite direction and the GPS interposition direction.

Note that, originally, a self-contained navigation track Tn is alsoformed of a plurality of self-contained navigation positions and aplurality of self-contained navigation directions; however, in thepresent embodiment, the sampling interval of self-contained navigationinformation is shorter than the sampling interval of GPS information, soFIG. 4A shows the self-contained navigation track Tn by the solid curvedarrow and illustrates a self-contained navigation position Np and aself-contained navigation direction Nd at only one position. That is, inthe self-contained navigation track Tn of FIG. 4A, the solid curvedarrow indicates that any one of the positions on the curve is theself-contained navigation position, the direction indicated by the arrowat the distal end of the curved arrow is the latest self-containednavigation direction, and the tangent of the curved arrow at eachself-contained navigation position indicates a self-contained navigationdirection at that self-contained navigation position.

As shown in FIG. 4A and FIG. 4B, generally, the self-containednavigation track Tn is similar to the GPS track but is different fromthe GPS track. GPS information not only depends on the relationshipbetween the vehicle and GPS satellites but also receives the influenceof multipath, and the like, so the GPS information is poor in regularityof error and can steeply change as compared with self-containednavigation information. On the other hand, an error of the outputinformation of the vehicle speed sensor 41 and an error of the outputinformation of the gyro sensor 42 regularly occur as compared with anerror of the GPS information, and the frequency of a steep variation inthe output information of the vehicle speed sensor 41 and the frequencyof a steep variation in the output information of the gyro sensor 42 arelow. Thus, an error of the self-contained navigation information Tnaccumulates over time; however, the degrees of reliability of pieces ofoutput information that are output at adjacent times do notsignificantly differ from each other. Therefore, the shape of theself-contained navigation track Tn is more accurate than that of the GPStrack. Then, the self-contained navigation track Tn is rotated andtranslated in a state where the shape of the self-contained navigationtrack In is maintained, and then the GPS track may be evaluated to havea higher degree of reliability as the GPS track has a higher degree ofcoincidence with self-contained navigation track Tn that is rotated andtranslated to have the highest degree of coincidence with the GPS track.In addition, when the degree of reliability of the GPS track is high andcan be a correction target track, the self-contained navigation track Tnis rotated and translated in a state where the shape of theself-contained navigation track Tn is maintained, and then the rotationangle and the translation amount by which the degree of coincidencebetween the self-contained navigation track Tn and the GPS track is thehighest may be respectively assumed as a first correction amount of theself-contained navigation direction and a first correction amount of theself-contained navigation position.

Then, in the present embodiment, the first correction amount of theself-contained navigation direction is statistically determined on thebasis of GPS satellite directions and GPS intercoordinate directions,which correspond to a plurality of GPS positions, and self-containednavigation directions, which correspond to a plurality of self-containednavigation positions. That is, a representative value of the directiondifferences between a plurality of GPS satellite directions and aplurality of self-contained navigation directions and a representativevalue of the direction differences between a plurality of GPSintercoordinate directions and a plurality of self-contained navigationdirections are assumed as the rotation angle of the self-containednavigation track Tn by which the degree of coincidence between theself-contained navigation track and the GPS track is the highest.

The pre-rotated self-contained navigation track Tn is actually formed ofa plurality of self-contained navigation positions Np and a plurality ofself-contained navigation directions Nd, so, when the directiondifference (rotation angle) between the self-contained navigationdirection Nd and the GPS direction (GPS satellite direction Gds and GPSintercoordinate direction Gdc) at the same time is determined, therotation angle by which the self-contained navigation track Tn isrotated at that time to obtain the highest degree of coincidence betweenthe GPS track and the self-contained navigation track Tn is determined.Thus, when a representative value of the direction differences betweenthe self-contained navigation directions Nd and the GPS directions atmultiple times is determined, the representative value may be assumed asthe rotation angle by which the degree of coincidence between the GPStrack and the self-contained navigation track Tn is the highest. In FIG.4C, the broken curved arrow indicates the pre-rotated self-containednavigation track Tn, and the alternate long and short dashed curvedarrow indicates a rotated self-contained navigation track Tnr. FIG. 4Cshows a rotation angle α by which the degree of coincidence between theGPS track and the self-contained navigation track Tn is the highest.

Furthermore, in the present embodiment, the first correction amount ofthe self-contained navigation position is statistically determined onthe basis of a plurality of GPS positions and a plurality ofself-contained navigation positions. That is, a representative value ofthe position differences between the plurality of GPS positions and theplurality of self-contained navigation positions is assumed as thetranslation amount of the self-contained navigation track by which thedegree of coincidence between the self-contained navigation track andthe GPS track is the highest. For example, FIG. 4C shows thepre-translated self-contained navigation track Tnr by the broken curvedarrow, and shows a translated self-contained navigation track Tnm by thesolid curved arrow.

The pre-translated self-contained navigation track Tnr is a trackobtained by rotating the self-contained navigation track by the abovedescribed rotation angle a, and is formed of a plurality of rotatedself-contained navigation positions and a plurality of rotatedself-contained navigation directions. Then, when the position difference(translation amount along x-axis and translation amount along y-axis)between the rotated self-contained navigation position and the GPSposition at the same time is determined, the rotated self-containednavigation track Tnr is translated to thereby determine the translationamount by which the degree of coincidence between the GPS track and theself-contained navigation track Tn is the highest at that time. Thus,when a representative value of the position differences between theself-contained navigation positions and the GPS positions at multipletimes is determined, the representative value may be assumed as thetranslation amount (X and Y shown in FIG. 4C) by which the degree ofcoincidence between the GPS track and the self-contained navigationtrack Tn is the highest.

The process of comparing the GPS track with the self-containednavigation track shown in FIG. 3 is a process of determining therotation angle and the translation amount as described above anddetermining the degree of reliability on the basis of the rotation angleand the translation amount. In order to execute the above process,first, the control unit 20 operates the self-contained navigationinformation correcting unit 21 d to acquire a travel distance from thetime point at which the process of comparing the GPS track with theself-contained navigation track shown in FIG. 3 is executed last timeand then determine whether the travel distance is longer than or equalto a predetermined distance (step S200). When it is determined in stepS200 that the travel distance is not longer than or equal to thepredetermined distance, the process of step S205 and the following stepsare skipped. That is, the comparing process is configured to be executedat an interval of the predetermined distance.

When it is determined in step S200 that the travel distance from thetime point at which the process of comparing the GPS track with theself-contained navigation track is executed last time is longer than orequal to the predetermined distance, the control unit 20 operates theGPS track acquisition unit 21 c to acquire a GPS track and operates theself-contained navigation track acquisition unit 21 a to acquire aself-contained navigation track (step S205). Subsequently, the controlunit 20 operates the self-contained navigation information correctingunit 21 d to acquire the direction differences between the GPS satellitedirections and the self-contained navigation directions (step S210).That is, the control unit 20 acquires GPS satellite directions andself-contained navigation directions at multiple positions on the basisof the pieces of GPS information and pieces of self-contained navigationinformation that are acquired within a predetermined period of time, andthen acquires the direction differences between the GPS satellitedirections and the self-contained navigation directions, each pair ofwhich are acquired at the same time.

Furthermore, the control unit 20 operates the self-contained navigationinformation correcting unit 21 d to generate a frequency distribution ofthe direction differences with a weight corresponding to a GPS accuracy(step S215). The accuracy of each GPS direction (GPS satellitedirection) is determined by the GPS accuracy information, so astatistical process for determining the direction difference between theGPS track and the self-contained navigation track is configured so thatGPS information more significantly contributes to determining thedirection difference as the accuracy of the GPS direction increases.Specifically, the control unit 20 acquires GPS accuracies, determinesthe frequency of each direction difference acquired in step S210 so thatthe frequency increases as the accuracy of a GPS direction increases,and then generates the frequency distribution. Note that the frequencyjust needs to be set so that the frequency increases as the accuracy ofa GPS direction increases, and, for example, the accuracy information ofa GPS direction, which is normalized to increase as the accuracyincreases, may be used as the frequency or the accuracy information of aGPS direction, which is multiplied by a predetermined coefficient, maybe used as the frequency.

FIG. 5A to FIG. 8D are views for illustrating the statistical processfor determining direction differences between GPS directions andself-contained navigation directions and a representative value of thedirection differences. In each of FIG. 5A, FIG. 6A, FIG. 7A and FIG. 8A,the straight arrows extending from the solid circle indicate directionswithin the coordinate system. FIG. 5B, FIG. 6B, FIG. 7B and FIG. 8B showthe frequency distributions respectively generated on the basis of thedirections shown in FIG. 5A, FIG. 6A, FIG. 7A and FIG. 8A. FIG. 5A toFIG. 6B show the statistical process on the GPS satellite directions andthe self-contained navigation directions.

That is, FIG. 5A and FIG. 5B show a GPS satellite direction Gds1 atcertain time and a self-contained navigation direction Nd1 at the sametime. In this example, the direction difference between theself-contained navigation direction Nd1 and the GPS satellite directionGds1 is 10°, the accuracy information of the GPS direction is 40, and 80that is a value obtained by multiplying the accuracy information of theGPS direction by 2 is set as the total frequency of the directiondifference 10°. Furthermore, in this example, the frequency is smoothedso that there is a single peak of the frequency distribution even with arelatively small number of samples, and the frequency of the directiondifference between the self-contained navigation direction Nd1 and theGPS satellite direction Gds1 is half the above total frequency.Moreover, the frequency of the direction difference that is obtained byadding 10° to the direction difference between the self-containednavigation direction Nd1 and the GPS satellite direction Gds1 is aquarter of the above total frequency, and the frequency of the directiondifference that is obtained by subtracting 10° from the directiondifference between the self-contained navigation direction Nd1 and theGPS satellite direction Gds1 is a quarter of the above total frequency.That is, the statistical process is executed to form a frequencydistribution (Pa shown in FIG. 5B) that has a significant frequency evenaround the direction difference between the self-contained navigationdirection Nd1 and the GPS satellite direction Gds1.

FIG. 6A and FIG. 6B show a GPS satellite direction Gds2 at timesubsequent to that of the GPS satellite direction Gds1 and aself-contained navigation direction Nd2 at the same time as that of theGPS satellite direction Gds2. In this example, the direction differencebetween the self-contained navigation direction Nd2 and the GPSsatellite direction Gds2 is 20°, and the accuracy information of the GPSdirection is 20. Thus, the total frequency of the direction difference20° is 40, and the frequency of 20° that is the direction differencebetween the self-contained navigation direction Nd2 and the GPSsatellite direction Gds2 is 20 (40×½). In addition, the frequency of thedirection difference that is obtained by adding 10° to 20° that is thedirection difference between the self-contained navigation direction Nd2and the GPS satellite direction Gds2 and the frequency of the directiondifference that is obtained by subtracting 10° from 20° that is thedirection difference between the self-contained navigation direction Nd2and the GPS satellite direction Gds2 are 10 (40×¼). FIG. 6B shows thethus generated frequency distribution Pb to be added to the frequencydistribution by hatching.

After the frequency distribution is generated on the basis of the GPSsatellite directions as described above, the control unit 20 executesthe process of adding frequencies based on the direction differencesbetween GPS intercoordinate directions and self-contained navigationdirections to the frequency distribution. Therefore, first, the controlunit 20 operates the self-contained navigation information correctingunit 21 d to acquire the direction differences between GPSintercoordinate directions and self-contained navigation directions(step S220). Specifically, the control unit 20 determines vectors eachof which connects adjacent two GPS positions on the basis of the piecesof GPS information acquired within a predetermined period of time,acquires GPS intercoordinate directions on the basis of the vectors,acquires self-contained navigation directions on the basis of the piecesof self-contained navigation information acquired within thepredetermined period of time, and acquires the direction differencesbetween the GPS intercoordinate directions and the self-containednavigation directions, each pair of which are acquired at the same time.

Furthermore, the control unit 20 operates the self-contained navigationinformation correcting unit 21 d to add the frequencies of the directiondifferences to the frequency distribution with a weight corresponding toa GPS accuracy (step S225). Each GPS intercoordinate direction isdetermined by adjacent two GPS positions, so the accuracy of each GPSintercoordinate direction depends on the accuracy of the adjacent twoGPS positions. Therefore, the accuracy of each GPS intercoordinatedirection is determined by the geometric mean of the GPS accuracies ofthe adjacent two GPS positions that are consulted when the GPSintercoordinate direction is determined. Then, the control unit 20determines the frequency of each direction difference acquired in stepS220 so that the frequency increases as the accuracy of the GPSintercoordinate direction increases, and then adds the determinedfrequency to the frequency distribution. Note that the frequency justneeds to be set so that the frequency increases as the GPS accuracyincreases. In this example, the above described geometric mean isdirectly used as the frequency.

FIG. 7A to FIG. 8B show the statistical process on the GPSintercoordinate directions and the self-contained navigation directions.That is, FIG. 7A and FIG. 7B show a GPS intercoordinate direction Gdc1at certain time and a self-contained navigation direction Nd1 at thesame time. This example shows a state where the direction differencebetween the self-contained navigation direction Nd1 and the GPSintercoordinate direction Gdc1 is −10°, the pieces of accuracyinformation of the GPS positions for determining the GPS intercoordinatedirection are 60 and 80 and, as a result, the accuracy information ofthe GPS intercoordinate direction is 69 ((60×80)^(1/2)). In this case,69 that is the accuracy information of the GPS intercoordinate directionis a total frequency of the direction difference −10°, and adistribution Pc that is generated so that the frequency of the directiondifference −10° is a value obtained by multiplying 69 by ½ and thefrequency of the direction difference −20° and the frequency of thedirection difference 0° are values obtained by multiplying 69 by ¼ isadded to the frequency distribution.

Similarly, FIG. 8A and FIG. 8B show a GPS intercoordinate direction Gdc2at time subsequent to that of the GPS intercoordinate direction Gdc1 anda self-contained navigation direction Nd2 at the same time as that ofthe GPS intercoordinate direction Gdc2. This example shows a state wherethe direction difference between the self-contained navigation directionNd2 and the GPS intercoordinate direction Gdc2 is 20°, the pieces ofaccuracy information of the GPS positions for determining the GPSintercoordinate direction are 80 and 100 and, as a result, the accuracyinformation of the GPS intercoordinate direction is 89 ((80×100)^(1/2)).In this case, 89 that is the accuracy information of the GPSintercoordinate direction is a total frequency of the directiondifference 20°, a frequency distribution Pd that is generated so thatthe frequency of the direction difference 20° is a value obtained bymultiplying 89 by ½ and the frequency of the direction difference 30°and the frequency of the direction difference 10° are values obtained bymultiplying 89 by ¼ is added to the frequency distribution. FIG. 7Bshows the frequency distribution Pc to be added to the frequencydistribution by hatching. FIG. 8B shows the frequency distribution Pd tobe added to the frequency distribution by hatching.

After that, the control unit 20 operates the self-contained navigationinformation correcting unit 21 d to acquire the rotation angle of theself-contained navigation track Tn (step S230). That is, the controlunit 20 determines a representative value of the direction differenceson the basis of the frequency distribution generated through the processof steps S215 and S225, and acquires the representative value as therotation angle of the self-contained navigation track Tn. Specifically,the control unit 20 assumes the direction difference having the highestfrequency in the frequency distribution generated through the process ofsteps S215 and S225 as a representative value of the directiondifferences between the self-contained navigation track Tn and the GPStrack, and then assumes the representative value as the rotation angle(rotation angle cc shown in FIG. 4C) when the self-contained navigationtrack is rotated so as to obtain the highest degree of coincidencebetween the self-contained navigation track and the GPS track. Thus, inthe present embodiment, the rotation angle is the first correctionamount of the self-contained navigation direction for obtaining thehighest degree of coincidence between the self-contained navigationtrack and the GPS track.

Furthermore, the control unit 20 operates the self-contained navigationinformation correcting unit 21 d to acquire the degree of reliability ofthe GPS direction (step S235). In the present embodiment, the controlunit 20 acquires the degree of reliability of the GPS direction on thebasis of the frequency distribution generated through the process ofsteps S215 and S225. Specifically, the control unit 20 determines thedirection difference having the highest frequency in the frequencydistribution generated through the process of steps S215 and S225, avariance of that direction difference and a total frequency of thefrequency distribution. Then, the degree of reliability of the GPSdirection is set so that the degree of reliability increases as thefrequency of the direction difference having the highest frequencyincreases, the degree of reliability increases as the variance of thedirection difference reduces and the degree of reliability increases asthe total frequency of the frequency distribution increases. Note that,in the present embodiment, the degree of reliability of the GPSdirection is defined in five levels. That is, a map (not shown) fordetermining the degree of reliability of the GPS direction on the basisof the frequency of the direction difference having the highestfrequency, the variance of the direction difference and the totalfrequency of the frequency distribution is prepared, and the controlunit 20 acquires the degree of reliability of the GPS direction on thebasis of the map.

Subsequently, the control unit 20 operates the self-contained navigationinformation correcting unit 21 d to rotate the self-contained navigationtrack (step S240). That is, the control unit 20 rotates theself-contained navigation track by the rotation angle acquired in stepS230 in a state where the shape of the self-contained navigation trackis maintained within the prescribed coordinate system. For example, asshown in FIG. 4C, the self-contained navigation track Tn is rotated bythe angle a about the most previous self-contained navigation positionin the self-contained navigation track Tn within the x-y coordinatesystem to acquire the self-contained navigation track Tnr.

After that, the control unit 20 operates the self-contained navigationinformation correcting unit 21 d to acquire the position differencesbetween the GPS positions and the self-contained navigation positions(step S245). That is, the control unit 20 acquires a plurality of GPSpositions and a plurality of self-contained navigation positions on thebasis of the pieces of GPS information acquired within a predeterminedperiod of time and the pieces of self-contained navigation informationrotated in step S240, and then acquires the position differences betweenthe GPS positions and the self-contained navigation positions, each pairof which are acquired at the same time.

Furthermore, the control unit 20 operates the self-contained navigationinformation correcting unit 21 d to generate a frequency distribution ofthe position differences with a weight corresponding to a GPS accuracy(step S250). That is, the accuracy of each GPS position is determined bythe GPS accuracy information, so GPS information more significantlycontributes to determining the position difference as the accuracy ofthe GPS position increases. Specifically, the control unit 20 acquiresGPS accuracies, determines the frequency of each position differenceacquired in step S245 so that the frequency increases as the accuracy ofa GPS position increases, and then generates a frequency distribution byadding the determined frequency to the frequency distribution. Note thatthe frequency of each position difference just needs to be set so thatthe frequency increases as the accuracy of a GPS position increases,and, for example, the accuracy information of a GPS position, which isnormalized to increase as the accuracy increases, may be used as thefrequency or the accuracy information of a GPS position, multiplied by apredetermined coefficient, may be used as the frequency.

FIG. 9A to FIG. 11B are views for illustrating the statistical processfor determining position differences between GPS positions andself-contained navigation positions and a representative value of theposition differences. In FIG. 9A, FIG. 10A and FIG. 11A, the solidcircles indicate positions within the coordinate system. FIG. 9B, FIG.10B and FIG. 11B show frequency distributions respectively generated onthe basis of the positions shown in FIG. 9A, FIG. 10A and FIG. 11A. FIG.9A and FIG. 9B show a GPS position Gp1 at certain time and aself-contained navigation position Np1 at the same time. In addition,FIG. 10A and FIG. 10B show a GPS position Gp2 at time subsequent to thatof the GPS position Gp1 and a self-contained navigation position Np2 atthe same time as that of the GPS position Gp2, and FIG. 11A and FIG. 11Bshow a GPS position Gp3 at time subsequent to the GPS position Gp2 and aself-contained navigation position Np3 at the same time as that of theGPS position Gp3.

As shown in these examples, the position difference between theself-contained navigation position Np1 and the GPS satellite positionGp1 is defined by a position difference Δx in the x-axis direction and aposition difference Δy in the y-axis direction, and a frequencydistribution is generated for a position difference in each axisdirection; however, FIG. 9B, FIG. 10B and FIG. 11B just illustrate aposition difference Δx in the x-axis direction. Of course, a positiondifference in the y-axis direction just differs from a positiondifference in the x-axis direction in a difference acquired as aposition difference, and the process of generating a frequencydistribution is almost the same.

For a position difference as well, a total frequency of positiondifferences is determined on the basis of the pieces of accuracyinformation of the GPS positions when a frequency distribution isgenerated, and the frequencies are smoothed so that there is a singlepeak of the frequency distribution even with a relatively small numberof samples. In the example shown in FIG. 9A and FIG. 9B, the positiondifference Δx between the self-contained navigation position Np1 and theGPS satellite position Gp1 is 80, and the accuracy information of theGPS position is 80. In the example shown in FIG. 10A and FIG. 10B, theposition difference Ax between the self-contained navigation positionNp2 and the GPS satellite position Gp2 is 60, and the accuracyinformation of the GPS position is 40. Furthermore, in the example shownin FIG. 11A and FIG. 11B, the position difference Δx between theself-contained navigation position Np3 and the GPS satellite positionGp3 is 40, and the accuracy information of the GPS position is 100.

For a GPS position, the accuracy information of the GPS position isconfigured to be a total frequency, and the accuracy information of theGPS position is 80 in FIG. 9A and FIG. 9B, so the total frequency of theposition difference Δx=80 between the self-contained navigation positionNp1 and the GPS position Gp1 is 80. Then, the frequency of the positiondifference Δx=80 is half the total frequency, and the frequency of theposition difference, obtained by adding 20 to the position difference Δxbetween the self-contained navigation position Np1 and the GPS satelliteposition Gp1, and the frequency of the position difference, obtained bysubtracting 20 from the position difference Δx between theself-contained navigation position Np1 and the GPS satellite positionGp1, each are a quarter of the total frequency. In this manner, afrequency distribution (Pe shown in FIG. 9B) that also has a significantfrequency around the position difference Δx between the self-containednavigation position Np1 and the GPS satellite position Gp1 is generated.

In FIG. 10A and FIG. 10B, the accuracy information of the GPS positionis 40, so the total frequency of the position difference Δx=60 betweenthe self-contained navigation position Np2 and the GPS position Gp2 is40. Then, a frequency distribution Pf is generated so that the frequencyof the position difference Δx=60 is half the total frequency and thefrequencies of the position differences Δx=40 and 80 each are a quarterof the total frequency. In FIG. 11A and FIG. 11B, the accuracyinformation of the GPS position is 100, so the total frequency of theposition difference Δx=40 between the self-contained navigation positionNp3 and the GPS position Gp3 is 100. Then, a frequency distribution Pgis generated so that the frequency of the position difference Δx=40 ishalf the total frequency and the frequencies of the position differencesΔx=20 and 60 each are a quarter of the total frequency. FIG. 9B, FIG.10B and FIG. 11B show the frequency distributions Pe to Pg to be addedto the frequency distribution by hatching.

After the frequency distribution is generated on the basis of the GPSpositions as described above, the control unit 20 operates theself-contained navigation information correcting unit 21 d to acquirethe translation amount of the self-contained navigation track (stepS255). That is, the control unit 20 determines a representative value ofthe position differences on the basis of the frequency distributiongenerated through the process of step S250, and then acquires therepresentative value as the translation amount of the self-containednavigation track. Specifically, the control unit 20 determines theposition difference having the highest frequency in the frequencydistribution generated through the process of step S250 for each of Δxand Δy, and then assumes each of the position differences as arepresentative value of the position difference between theself-contained navigation track and the GPS track. Then, the controlunit 20 assumes the respective representative values as the translationamount in the x-axis direction and the translation amount in the y-axisdirection (X and Y shown in FIG. 4C) when the self-contained navigationtrack is translated so as to obtain the highest degree of coincidencebetween the self-contained navigation track and the GPS track. Thus, inthe present embodiment, the translation amount in the x-axis directionand the translation amount in the y-axis direction correspond to thefirst correction amount of the self-contained navigation positions forobtaining the highest degree of coincidence between the self-containednavigation track and the GPS track.

Furthermore, the control unit 20 operates the self-contained navigationinformation correcting unit 21 d to acquire the degree of reliability ofthe GPS position (step S260). In the present embodiment, the controlunit 20 acquires the degree of reliability of the GPS position on thebasis of the frequency distribution generated through the process ofstep S250. Specifically, the control unit 20 determines the positiondifference having the highest frequency in the frequency distributiongenerated through the process of step S250, a variance of that positiondifference and a total frequency of the frequency distribution. Then,the degree of reliability of the GPS position is set so that the degreeof reliability increases as the frequency of the position differencehaving the highest frequency increases, the degree of reliabilityincreases as the variance of the position difference reduces and thedegree of reliability increases as the total frequency of the frequencydistribution increases. Note that, in the present embodiment, the degreeof reliability of the GPS position is defined in five levels. That is, amap (not shown) for determining the degree of reliability of the GPSposition on the basis of the frequency of the position difference havingthe highest frequency, the variance of the position difference and thetotal frequency of the frequency distribution is prepared, and thecontrol unit 20 acquires the degree of reliability of the GPS positionon the basis of the map.

The thus described degrees of reliability of the GPS direction and GPSposition are respectively determined on the basis of the statistics onthe plurality of GPS directions and the plurality of GPS positions, sothe degrees of reliability of the GPS direction and GPS positionindicate the degree of reliability of the GPS track. On the other hand,GPS accuracy information indicates the accuracy of each GPS directionand the accuracy of each GPS position. Thus, the degree of reliabilityof each of the GPS direction and the GPS position is determined throughstatistical process based on the pieces of GPS accuracy information, andthe degree of reliability of a track determined from the pieces of GPSinformation may be defined by the degree of reliability of each of theGPS direction and the GPS position. Note that a method of determiningthe degree of reliability is not limited to the above describedtechnique; for example, GPS accuracy information may be used as thedegree of reliability.

When the process of comparing the GPS track with the self-containednavigation track in this way, the control unit 20 returns to the processshown in FIG. 2A and FIG. 2B. That is, the control unit 20 operates theself-contained navigation information correcting unit 21 d to comparethe degree of reliability of the GPS direction with the degree ofreliability of the matching direction and then determine whether thedegree of reliability of the GPS direction is higher than or equal tothe degree of reliability of the matching direction (step S110). Then,when it is determined in step S110 that the degree of reliability of theGPS direction is higher than or equal to the degree of reliability ofthe matching direction, the control unit 20 uses the GPS track as acorrection target track to set a direction correction target (stepS115). That is, the control unit 20 rotates the self-containednavigation track by the rotation angle acquired in step S230, translatesthe self-contained navigation track by the translation amount acquiredin step S255, and sets a direction oriented as a result of rotation andtranslation of the self-contained navigation direction at the latesttime point as the direction correction target. For example, in therotated and translated self-contained navigation track Turn as shown inFIG. 4C, the direction in which the distal end of the arrow is orientedis the direction oriented as a result of rotation and translation of theself-contained navigation direction at the latest time point, so thedirection in which the distal end of the arrow is oriented is thedirection correction target.

On the other hand, when it is determined in step S110 that the degree ofreliability of the GPS direction is not higher than or equal to thedegree of reliability of the matching direction, the control unit 20uses the matching track as a correction target track to set a directioncorrection target (step S120). That is, the control unit 20 sets thematching direction as the correction target direction.

Subsequently, the control unit 20 operates the self-contained navigationinformation correcting unit 21 d to compare the degree of reliability ofthe GPS position with the degree of reliability of the matching positionand then determine whether the degree of reliability of the GPS positionis higher than or equal to the degree of reliability of the matchingposition (step S125). Then, when it is determined in step S125 that thedegree of reliability of the GPS position is higher than or equal to thedegree of reliability of the matching position, the control unit 20 usesthe GPS track as a correction target track to set a position correctiontarget (step S130). That is, the control unit 20 rotates theself-contained navigation track by the rotation angle acquired in stepS230, translates the self-contained navigation track by the translationamount acquired in step S255, and uses a position resulting fromrotation and translation of the self-contained navigation position atthe latest time point as the position correction target. For example, inthe rotated and translated self-contained navigation track Tnm as shownin FIG. 4C, the position (position indicated by the outline circle inFIG. 4C) of the distal end of the arrow is the position resulting fromrotation and translation of the self-contained navigation position atthe latest time point, so the position at which the distal end of thearrow is present is the position correction target.

On the other hand, when it is determined in step S125 that the degree ofreliability of the GPS position is not higher than or equal to thedegree of reliability of the matching position, the control unit 20 usesthe matching track as a correction target track to set a positioncorrection target (step S135). That is, the control unit 20 uses thematching position as the correction target position.

After that, the control unit 20 operates the self-contained navigationinformation correcting unit 21 d to acquire the degree of reliability ofthe correction target (step S140). In the present embodiment, thecorrection target is set for each of the direction and the position, sothe degree of reliability is acquired for each of the direction and theposition. Here, the degree of reliability of the correction targetcorresponds to the degree of reliability of the correction target track.Thus, the degree of reliability of the GPS position in the case wherestep S115 is executed or the degree of reliability of the matchingposition in the case where step S120 is executed is acquired as thedegree of reliability of the position correction target. In addition,the degree of reliability of the GPS direction in the case where stepS130 is executed or the degree of reliability of the matching directionin the case where step S135 is executed is acquired as the degree ofreliability of the direction correction target.

Furthermore, the control unit 20 operates the self-contained navigationinformation correcting unit 21 d to execute the self-containednavigation information correcting process for correcting theself-contained navigation direction and the self-contained navigationposition (step S145). FIG. 12 is a flowchart that shows theself-contained navigation information correcting process. In theself-contained navigation information correcting process, the controlunit 20 first acquires the second correction amount of theself-contained navigation position (step S300). In the presentembodiment, the second correction amount of the self-containednavigation position is determined on the basis of the degree ofreliability of the correction target track (GPS track or matchingtrack), a value obtained by subtracting the degree of reliability of theself-contained navigation track from the degree of reliability of thecorrection target track and the first correction amount of theself-contained navigation position.

Specifically, a map (not shown) defines that the second correctionamount of the self-contained navigation position increases as the degreeof reliability of the correction target track increases, the secondcorrection amount of the self-contained navigation position increases asthe value obtained by subtracting the degree of reliability of theself-contained navigation track from the degree of reliability of thecorrection target track increases, and the second correction amount ofthe self-contained navigation position increases as the first correctionamount of the self-contained navigation position increases. However, inthe map, the second correction amount of the self-contained navigationposition is smaller than the first correction amount. The control unit20 acquires the second correction amount of the self-containednavigation position on the basis of the map.

That is, as the degree of reliability of the correction target trackincreases, the probability of erroneously correcting the self-containednavigation track so as to coincide with the correction target trackdecreases. Then, the second correction amount of the self-containednavigation position is set so as to increase as the degree ofreliability of the GPS track increases. By so doing, it is possible toreduce the probability of occurrence of erroneous correction and earlyimprove the accuracy of the self-contained navigation track.

In addition, the correction target track is a reference used todetermine the first correction amount of the self-contained navigationposition for obtaining the highest degree of coincidence between theself-contained navigation track and the correction target track, and theself-contained navigation track is a correction subject. Thus, the valueobtained by subtracting the degree of reliability of the self-containednavigation track from the degree of reliability of the correction targettrack is a value obtained by subtracting the degree of reliability ofthe correction subject from the degree of reliability of the correctionreference, and that value increases as the degree of reliability of thecorrection reference becomes higher than the degree of reliability ofthe correction subject. Then, the second correction amount of theself-contained navigation position is set so as to increase with anincrease in the value obtained by subtracting the degree of reliabilityof the self-contained navigation track from the degree of reliability ofthe correction target track. By so doing, it is possible to reduce theprobability of occurrence of erroneous correction and early improve theaccuracy of the self-contained navigation track. Note that the degree ofreliability of the self-contained navigation track just needs toindicate the degree of reliability of information, such as theself-contained navigation position and the self-contained navigationdirection. In the present embodiment, the self-contained navigationposition and the self-contained navigation direction are repeatedlycorrected, and the correction reference consulted in a previouscorrection is a previous correction target track. Thus, in the presentembodiment, after a correction is performed, the degree of reliabilityof a previous correction target track used as the correction referenceis assumed as the degree of reliability of each of the correctedself-contained navigation position and the corrected self-containednavigation direction.

Furthermore, the first correction amount of the self-containednavigation position indicates the degree of difference between theself-contained navigation track and the correction target track. Then,the second correction amount of the self-contained navigation positionis set so as to increase with an increase in the difference between theself-contained navigation track and the correction target track. By sodoing, it is possible to early improve the accuracy of theself-contained navigation track. Note that, in the present embodiment,the degree of reliability of the correction target track and the degreeof reliability of the self-contained navigation track each are definedin five levels. Therefore, it is only necessary that the secondcorrection amount of the self-contained navigation position increases ina stepwise manner as the degree of reliability of the correction targettrack increases and the second correction amount of the self-containednavigation position increases in a stepwise manner as the value obtainedby subtracting the degree of reliability of the self-containednavigation track from the degree of reliability of the correction targettrack increases. In addition, it is also applicable that the secondcorrection amount of the self-contained navigation position variescontinuously or varies in a stepwise manner in accordance with the firstcorrection amount of the self-contained navigation position.

Here, it is only necessary that the second correction amount tends toincrease as the degree of reliability of the correction target trackincreases, the second correction amount tends to increase as the valueobtained by subtracting the degree of reliability of the self-containednavigation track from the degree of reliability of the correction targettrack increases and the second correction amount tends to increase asthe first correction amount of the self-contained navigation positionincreases. Thus, it is applicable that the second correction amountvaries in m levels (m is a natural number) with a variation in thedegree of reliability in n levels (n is a natural number). Furthermore,the second correction amount may be determined on the basis of any oneof or a combination of any two of the degree of reliability of thecorrection target track, the value obtained by subtracting the degree ofreliability of the self-contained navigation track from the degree ofreliability of the correction target track and the first correctionamount of the self-contained navigation position.

In the above described manner, when the second correction amount of theself-contained navigation position is acquired in step S300, the controlunit 20 operates the self-contained navigation information correctingunit 21 d to determine whether the second correction amount of theself-contained navigation position is larger than 0 (step S305), andthen, when it is determined in step S305 that the second correctionamount of the self-contained navigation position is not larger than 0,the control unit 20 skips step S310.

When it is determined in step S305 that the second correction amount ofthe self-contained navigation position is larger than 0, the controlunit 20 corrects the self-contained navigation position using the secondcorrection amount of the self-contained navigation position (step S310).FIG. 13A is a view that illustrates a manner of correcting theself-contained navigation position using the second correction amount ofthe self-contained navigation position. In FIG. 13A, an example of aposition correction target Gp in the case where the correction targettrack is a GPS track is indicated by the alternate long and short dashedline circle, and the pre-corrected self-contained navigation position Npis indicated by the broken line circle. In this example, the firstcorrection amount of the self-contained navigation position Np is A1,and the second correction amount is A2.

As shown in FIG. 13A, the second correction amount A2 is set so as toachieve part of a correction achieved by the first correction amount A1and is smaller than the first correction amount A1. That is, acorrection achieved by the first correction amount A1 is, for example, acorrection such that the self-contained navigation position Np istranslated along a vector V1 directed from the self-contained navigationposition Np toward the correction target Gp, and the vector V1, forexample, has a length of X along x-axis and a length of Y along y-axisin the example shown in FIG. 4C. On the other hand, the secondcorrection amount A2 corresponds to a correction such that theself-contained navigation position Np is translated along a vector V2obtained by multiplying the vector V1 by a coefficient C (0<C<1). Thecoefficient C is determined in the above described step S310. Thus, forexample, in the example shown in FIG. 4C, a correction using the secondcorrection amount A2 is determined by multiplying each of X and Y by thecoefficient C that indicates the second correction amount, and thecorrected self-contained navigation position Npa is determined asindicated by the solid line circle. In the above correction, the controlunit 20 corrects the self-contained navigation position using the secondcorrection amount A2 that is smaller than the first correction amount,which is the correction amount of the self-contained navigation positionfor obtaining the highest degree of coincidence between theself-contained navigation track and the correction target track. Thus,even if an erroneous correction is performed, a correction may beperformed so as to suppress the influence thereof, so it is possible toeasily improve the accuracy of the self-contained navigation track.

Subsequently, the control unit 20 corrects the self-contained navigationdirection in steps S315 and S320. In the present embodiment, the controlunit 20 is configured to correct the self-contained navigation directionby a constant correction amount. Then, the control unit 20 operates theself-contained navigation information correcting unit 21 d to determinewhether the degree of reliability of the direction correction targetsatisfies a predetermined reference (step S315). In the presentembodiment, the control unit 20 determines that the degree ofreliability of the direction correction target satisfies thepredetermined criteria when the degree of reliability of the directioncorrection target is higher than or equal to a predetermined minimumdegree of reliability required as the correction reference.

Then, when it is determined in step S315 that the degree of reliabilityof the direction correction target does not satisfy the predeterminedcriteria, the control unit 20 skips step S320. On the other hand, whenit is determined in step S315 that the degree of reliability of thedirection correction target satisfies the predetermined criteria, thecontrol unit 20 operates the self-contained navigation informationcorrecting unit 21 d to correct the self-contained navigation directionusing the second correction amount of the self-contained navigationdirection (step S320). Here, the second correction amount of theself-contained navigation direction is a constant value. For example,when the first correction amount is larger than 1°, the secondcorrection amount is set at 1°, or the like; whereas, when the firstcorrection amount is smaller than or equal to 1°, the second correctionamount is set at 0°, or the like.

FIG. 13B is a view that illustrates a manner of correcting theself-contained navigation direction using the second correction amountof the self-contained navigation direction. In FIG. 13B, a directioncorrection target Gd in the case where the correction target track is aGPS track is illustrated by the alternate long and short dashed straightarrow, and the pre-corrected self-contained navigation direction Nd isillustrated by the broken straight arrow. In this example, the firstcorrection amount of the self-contained navigation direction Nd is A1and the second correction amount of the self-contained navigationdirection Nd is A2.

That is, a correction achieved by the first correction amount A1 is, forexample, a correction such that the self-contained navigation directionNd is rotated to coincide with the correction target Gd, and therotation angle is, for example, the rotation angle a in the exampleshown in FIG. 4C. On the other hand, a correction achieved by the secondcorrection amount A2 is, for example, a correction such that theself-contained navigation direction Nd is rotated by 1° to approach thecorrection target Gd. In the above described correction, the controlunit 20 corrects the self-contained navigation direction using theconstant second correction amount A2 that is smaller than the firstcorrection amount A1, which is the correction amount of theself-contained navigation direction for obtaining the highest degree ofcoincidence between the self-contained navigation track and thecorrection target track. Thus, it is possible to improve the accuracy ofthe self-contained navigation track in a state where the influence dueto an erroneous correction is considerably minimized.

When the self-contained navigation information is corrected through theabove process, the control unit 20 returns to the process shown in FIG.2A and FIG. 2B, and then operates the self-contained navigationinformation correcting unit 21 d to update the degree of reliability ofthe self-contained navigation information (step S150). That is, thecontrol unit 20 uses the degree of reliability of the positioncorrection target acquired in step S140 as the degree of reliability ofthe self-contained navigation position, and uses the degree ofreliability of the direction correction target acquired in step S140 asthe degree of reliability of the self-contained navigation direction.

As described above, self-contained navigation information just needs tobe corrected using the second correction amount that is smaller than thefirst correction amount of the self-contained navigation information,acquired by comparing the self-contained navigation track with the GPStrack, for obtaining the highest degree of coincidence between theself-contained navigation track and the GPS track. By determining thedifference between the self-contained navigation track and the GPS trackthrough comparison therebetween, it is possible to determine acorrection that should be performed on the self-contained navigationinformation in order to minimize the difference between theself-contained navigation track and the GPS track to thereby obtain thehighest degree of coincidence therebetween. For example, it isapplicable that the self-contained navigation track is rotated andtranslated so as to obtain the highest degree of coincidence between theself-contained navigation track and the GPS track, self-containednavigation information that indicates the rotated and translatedself-contained navigation track is set as a correction target and then acorrection amount for bringing the current self-contained navigationinformation into coincidence with the correction target is set as thefirst correction amount.

That is, when the self-contained navigation track is rotated andtranslated to obtain the highest degree of coincidence between theself-contained navigation track and the GPS track, the self-containednavigation information may be regarded as being inaccurate by thephysical quantities corresponding to the rotation and translation. Then,when the self-contained navigation information that indicates therotated and translated self-contained navigation track is set as acorrection target and then a correction amount for bringing thecorrection target and the self-contained navigation information intocoincidence is set as the first correction amount, the accuracy of theself-contained navigation track may be improved by correcting theself-contained navigation information using the second correction amountthat is smaller than the first correction amount. Note that, when thecorrection using the second correction amount that is smaller than thefirst correction amount is repeatedly performed, it is possible togradually bring the self-contained navigation track close to the GPStrack. In addition, even if an erroneous correction is performed becauseof a large error of the GPS track, it is possible to suppress theinfluence of the erroneous correction rather than a correction foreliminating the difference between the self-contained navigation trackand the GPS track at a time is performed.

Furthermore, the second correction amount may be selected as long as thesecond correction amount is smaller than the first correction amount,and, as a configuration example for determining the second correctionamount, the self-contained navigation information may be corrected usingthe second correction amount that increases as the degree of reliabilityof the GPS track increases. As the degree of reliability of the GPStrack formed of time-series GPS information increases, the probabilityof erroneously correcting the self-contained navigation track so as tocoincide with the GPS track decreases. Then, the second correctionamount is set so as to increase as the degree of reliability of the GPStrack increases. By so doing, it is possible to suppress the probabilityof occurrence of erroneous correction and early improve the accuracy ofthe self-contained navigation track.

Note that the degree of reliability of the GPS track just needs toindicate the reliability of information, such as the position anddirection of the vehicle, indicated by the GPS track and, for example,the degree of reliability of the GPS track may be determined bycomparing the self-contained navigation track with the GPS track. Anerror of the self-contained navigation information regularly occurs ascompared with an error of the GPS information, and is less likely tosteeply vary. Thus, an error of the self-contained navigationinformation accumulates over time; however, the degrees of reliabilityof pieces of self-contained navigation information that are output atadjacent times do not significantly differ from each other. Therefore,the shape of the self-contained navigation track indicated bytime-series self-contained navigation information of the sensors isaccurate.

That is, the GPS track may be regarded as being accurate as the degreeof coincidence in shape between the self-contained navigation track andthe GPS track increases. Then, it is possible to define the degree ofreliability of the GPS track so that the degree of reliability of theGPS track increases as the degree of coincidence I shape increases. Inaddition, here, the second correction amount just needs to be set so asto tend to increase as the degree of reliability of the GPS trackincreases, the second correction amount may vary continuously or mayvary in a stepwise manner in accordance with the degree of reliabilityof the GPS track.

Furthermore, the second correction amount may be determined on the basisof the degree of reliability of the self-contained navigation track. Forexample, the self-contained navigation information may be correctedusing the second correction amount that increases as a value obtained bysubtracting the degree of reliability of the self-contained navigationtrack from the degree of reliability of the GPS track increases. The GPStrack is a reference that is used to determine the first correctionamount for obtaining the highest degree of coincidence between theself-contained navigation track and the GPS track, and theself-contained navigation track is a correction subject. Thus, the valueobtained by subtracting the degree of reliability of the self-containednavigation track from the degree of reliability of the GPS track is avalue obtained by subtracting the degree of reliability of thecorrection subject from the degree of reliability of the correctionreference, and that value increases as the degree of reliability of thecorrection reference becomes higher than the degree of reliability ofthe correction subject. Then, when the second correction amount is setso as to increase with an increase in the value obtained by subtractingthe degree of reliability of the self-contained navigation track fromthe degree of reliability of the GPS track, it is possible to reduce theprobability of occurrence of erroneous correction and early improve theaccuracy of the self-contained navigation track.

Note that the degree of reliability of the self-contained navigationtrack just needs to indicate the degree of reliability of information,such as the position and direction of the vehicle, indicated by theself-contained navigation track and, for example, the degree ofreliability of information (GPS track, or the like) that is thecorrection reference when a correction is performed may be used as thedegree of reliability of the corrected self-contained navigation track.Of course, here as well, the second correction amount just needs to beset so as to tend to increase with an increase in the value obtained bysubtracting the degree of reliability of the GPS track from the degreeof reliability of the self-contained navigation track. Thus, the secondcorrection amount may vary continuously or may vary in a stepwise mannerin accordance with the value obtained by subtracting the degree ofreliability of the GPS track from the degree of reliability of theself-contained navigation track.

Furthermore, the self-contained navigation information may be correctedusing the second correction amount that increases as the firstcorrection amount increases. The first correction amount indicates thedegree of difference between the self-contained navigation track and theGPS track. Then, the second correction amount is set so as to increasewith an increase in the difference between the self-contained navigationtrack and the GPS track. By so doing, it is possible to early improvethe accuracy of the self-contained navigation track. Here as well, thesecond correction amount just needs to be set so as to tend to increaseas the first correction amount increases, and the second correctionamount may vary continuously or may vary in a stepwise manner inaccordance with the first correction amount.

Furthermore, it is applicable that the self-contained navigationinformation is corrected using a constant second correction amount thatis smaller than the first correction amount when the degree ofreliability of the GPS track satisfies a predetermined criteria. Thatis, when the degree of reliability of the GPS track that is a correctionreference satisfies a predetermined criteria and the correctionreference ensures a certain level of reliability, the self-containednavigation information is corrected using a constant correction amount.With the above configuration, it is possible to improve the accuracy ofthe self-contained navigation track in a state where the influence dueto an erroneous correction is considerably minimized.

As described above, the second correction amount may vary with thedegree of reliability of the GPS track, or the like, or may be fixed. Inaddition, the characteristic of the second correction amount may bechanged in response to the characteristic of the GPS information. Forexample, it is applicable that, when the self-contained navigationinformation that indicates the position of the vehicle is corrected, thedegree of reliability of information that indicates the position of thevehicle and that is included in the GPS track is determined and then thesecond correction amount is adjusted in accordance with the degree ofreliability of the information that indicates the position of thevehicle. In addition, it is applicable that, when the self-containednavigation information that indicates the direction of the vehicle iscorrected, the degree of reliability of information that indicates thedirection of the vehicle and that is included in the GPS track isdetermined and then, when the degree of reliability of the informationthat indicates the direction of the vehicle satisfies a predeterminedcriteria, the self-contained navigation information is corrected using aconstant second correction amount that is smaller than the firstcorrection amount.

(3) Alternative Embodiments

The above embodiment is one example for carrying out the aspect of thepresent invention, and other various embodiments may be employed. Forexample, it is applicable that a GPS track is used as a correctiontarget track as long as the degree of reliability of the GPS track ishigh so that the GPS track may be used as a correction reference. Thatis, it is applicable that a GPS track is used as a correction targettrack when the degree of reliability of the GPS track exceeds apredetermined reference, a matching track is used as a correction targettrack when the degree of reliability of the GPS track is lower than thepredetermined reference, and self-contained navigation information iscorrected so as to reduce the difference between a self-containednavigation track and the correction target track.

Such a configuration may be implemented in such a manner that steps S110and S125 in FIG. 2A and FIG. 2B are modified in the above describedembodiment. Specifically, the control unit 20 determines in step S110whether the degree of reliability of a GPS direction satisfies apredetermined reference, executes step S115 when the degree ofreliability of the GPS direction satisfies the predetermined reference,and executes step S120 when the degree of reliability of the GPSdirection does not satisfy the predetermined reference. In addition, thecontrol unit 20 determines in step S125 whether the degree ofreliability of a GPS position satisfies a predetermined reference,executes step S130 when the degree of reliability of the GPS positionsatisfies the predetermined reference, and executes step S135 when thedegree of reliability of the GPS position does not satisfy thepredetermined reference. Note that the predetermined reference justneeds to be a reference for determining whether the accuracy of theself-contained navigation information may be improved when the GPS trackis used as a correction target track to correct the self-containednavigation information and, for example, it is applicable that a lowerlimit is set for the degree of reliability and then it is determinedwhether the degree of reliability is higher than or equal to the lowerlimit.

With the above configuration, the GPS track is used as a correctiontarget track when the degree of reliability of the GPS track is high. Byso doing, it is possible to correct the self-contained navigationinformation on the basis of further objective information. That is, aGPS track is generated on the basis of GPS information, and the GPSinformation does not depend on self-contained navigation information buta matching track depends on self-contained navigation informationbecause the matching track is determined on the basis of a comparisonbetween a self-contained navigation track and the shape of a roadindicated by map information. Thus, when the degree of reliability ofGPS information is high and accurate, the GPS information is appropriateas a reference used to correct the self-contained navigationinformation. Then, when the degree of reliability of a GPS track exceedsa predetermined reference, a reference used to correct theself-contained navigation information is set to the GPS track. By sodoing, it is possible to correct the self-contained navigationinformation on the basis of information that has a high reliability andthat does not depend on the self-contained navigation information.

Furthermore, in the above described embodiment, any one of the GPS trackand the matching track is selected as a correction target track on thebasis of the degree of reliability; however, when both the GPS track andthe matching track have a low degree of reliability such that it is notappropriate as a correction reference (the accuracy of theself-contained navigation information is not improved even when acorrection is performed), no correction may be performed.

Furthermore, in the configuration that a GPS track is used as acorrection target track when the degree of reliability of the GPS trackexceeds a predetermined reference, it is not necessary to determine thedegree of reliability of a matching track in order to determine acorrection target track. In addition, it is applicable that the degreeof reliability of a matching track is determined for a purpose otherthan the purpose of determining a correction target track. For example,when a matching track is used as a correction target track, the degreeof reliability of the matching track may be determined in order todetermine the degree of reliability of the corrected self-containednavigation track or the degree of reliability of a matching track may bedetermined in order to determine whether the matching track has a lowdegree of reliability such that it is not appropriate as a correctionreference.

Furthermore, in the above described embodiment, a position correctiontarget and a direction correction target are set on the basis of acorrection target track, a second correction amount is set so as togradually approach the correction targets, and then self-containednavigation information is corrected; instead, self-contained navigationinformation may be corrected without setting a specific correctiontarget. For example, it is applicable that the rotation angle andtranslation amount of a self-contained navigation track are determinedso that at least the self-contained navigation track approaches acorrection target track and then self-contained navigation informationis corrected so as to rotate and translate the self-contained navigationtrack in correspondence with the determined rotation angle and thedetermined translation amount.

Furthermore, in the above described embodiment, the degree ofreliability is defined separately for a position and a direction and acorrection is performed in a state where different types of tracks maybe respective correction references for a position and a direction;instead, a correction may be configured so that a correction referenceis a single type of track. For example, it is applicable that the degreeof reliability of each of a GPS position, a GPS direction, a matchingposition and a matching direction is defined and then, when the degreeof reliability of the GPS position has the highest degree ofreliability, a direction correction target is set to the GPS directionto thereby use only the GPS track as a correction reference.

Furthermore, in the above described embodiment, a GPS direction isdetermined on the basis of a GPS satellite direction and a GPSintercoordinate direction; instead, any one of a GPS satellite directionand a GPS intercoordinate direction may be used as a GPS direction.Furthermore, in the above described embodiment, the second correctionamounts for a position and a direction are respectively determined bydifferent techniques; instead, the second correction amounts may bedetermined by the same technique or the second correction amounts may berespectively determined by techniques inverse to those of the abovedescribed embodiment. For example, it is applicable that the secondcorrection amount for a position is a constant translation amount andthe second correction amount for a direction may increase as the degreeof reliability of a correction target track increases, the secondcorrection amount for a direction increases as a value obtained bysubtracting the degree of reliability of a self-contained navigationtrack from the degree of reliability of the correction target trackincreases and the second correction amount for a direction increases asthe first correction amount of the self-contained navigation directionincreases.

Furthermore, another sensor, such as an acceleration sensor, may beadded as a sensor for acquiring self-contained navigation information.Furthermore, a representative value of GPS positions and arepresentative value of GPS directions each may be a statistical mean ora statistical median. Moreover, the process of comparing aself-contained navigation track with a GPS track may be changed inaccordance with the accuracy of GPS information. For example, it isapplicable that a self-contained navigation track is compared with a GPStrack in a distance that is reduced as the accuracy of GPS informationindicated by GPS accuracy information increases. In the self-containednavigation track, accumulated errors increase over time, so, when theaccuracy of GPS information is high, a GPS track is compared with aself-contained navigation track while the accuracy of GPS informationremains high rather than a large number of pieces of time-series GPSinformation are acquired to increase the statistical accuracy. Then,when a self-contained navigation track is compared with a GPS track in adistance that is reduced as the accuracy of GPS information increases,it is possible to easily increase the accuracy of the self-containednavigation track.

Furthermore, the above described technique for correcting theself-contained navigation information using a correction amount that issmaller than a correction amount for obtaining the highest degree ofcoincidence between a time-series self-contained navigation track and atime-series GPS track may also be applied as a program or a method. Inaddition, the above described device, program and method may beimplemented as a sole device or may be implemented by utilizing acomponent shared with various portions provided for a vehicle, and areimplemented in various forms. For example, it is possible to provide anavigation system, a navigation method and a program that are providedwith the device described in the above embodiment. In addition, thedevice described in the above embodiment may be modified whereappropriate, for example, part of the device is software and part of thedevice is hardware. Furthermore, the aspect of the invention may beimplemented as a storage medium storing a program that controls thedevice. Of course, the storage medium storing software may be a magneticstorage medium or may be a magnetooptical storage medium, and anystorage media that will be developed in the future may also be usedsimilarly.

1. A track information generating device comprising: a self-containednavigation track acquisition unit that acquires a self-containednavigation track that is a track of a vehicle, indicated by time-seriespieces of self-contained navigation information; a GPS track acquisitionunit that acquires a GPS track that is a track of the vehicle, indicatedby time-series pieces of GPS information; and a self-containednavigation information correcting unit that compares the self-containednavigation track with the GPS track to acquire a first correction amountfor obtaining the highest degree of coincidence between theself-contained navigation track and the GPS track and then to correctthe self-contained navigation information using a second correctionamount that is smaller than the first correction amount.
 2. The trackinformation generating device according to claim 1, wherein theself-contained navigation information correcting unit acquires a degreeof reliability of the GPS track, and the self-contained navigationinformation correcting unit corrects the self-contained navigationinformation using the second correction amount that increases as thedegree of reliability of the GPS track increases.
 3. The trackinformation generating device according to claim 2, wherein theself-contained navigation information correcting unit compares theself-contained navigation track with the GPS track to acquire the degreeof reliability of the GPS track.
 4. The track information generatingdevice according to claim 1, wherein the self-contained navigationinformation correcting unit acquires a degree of reliability of the GPStrack and a degree of reliability of the self-contained navigationtrack, and the self-contained navigation information correcting unitcorrects the self-contained navigation information using the secondcorrection amount that increases as a value obtained by subtracting thedegree of reliability of the self-contained navigation track from thedegree of reliability of the GPS track increases.
 5. The trackinformation generating device according to claim 4, wherein theself-contained navigation information correcting unit compares theself-contained navigation track with the GPS track to acquire the degreeof reliability of the GPS track.
 6. The track information generatingdevice according to claim 1, wherein the self-contained navigationinformation correcting unit corrects the self-contained navigationinformation using the second correction amount that increases as thefirst correction amount increases.
 7. The track information generatingdevice according to claim 1, wherein the self-contained navigationinformation correcting unit acquires a degree of reliability of the GPStrack, and the self-contained navigation information correcting unitcorrects the self-contained navigation information using the constantsecond correction amount that is smaller than the first correctionamount when the degree of reliability of the GPS track satisfies apredetermined criteria.
 8. The track information generating deviceaccording to claim 7, wherein the self-contained navigation informationcorrecting unit compares the self-contained navigation track with theGPS track to acquire the degree of reliability of the GPS track.
 9. Atrack information generating method comprising: acquiring aself-contained navigation track that is a track of a vehicle, indicatedby time-series pieces of self-contained navigation information;acquiring a GPS track that is a track of the vehicle, indicated bytime-series pieces of GPS information; and comparing the self-containednavigation track with the GPS track to acquire a first correction amountfor obtaining the highest degree of coincidence between theself-contained navigation track and the GPS track and then to correctthe self-contained navigation information using a second correctionamount that is smaller than the first correction amount.
 10. Acomputer-readable storage medium that stores computer-executableinstructions for performing a track information generating methodcomprising: acquiring a self-contained navigation track that is a trackof a vehicle, indicated by time-series pieces of self-containednavigation information; acquiring a GPS track that is a track of thevehicle, indicated by time-series pieces of GPS information; andcomparing the self-contained navigation track with the GPS track toacquire a first correction amount for obtaining the highest degree ofcoincidence between the self-contained navigation track and the GPStrack and then to correct the self-contained navigation informationusing a second correction amount that is smaller than the firstcorrection amount.